[ARROW-11882] [Rust] Implement Debug printing "kernel"

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Invalid
• Component/s: Rust
• External issue URL: https://github.com/apache/arrow/issues/27724
• Assignee: Unassigned
• Reporter: Andrew Lamb
• Created: 05/Mar/21 21:50
• Updated: 11/Jan/23 08:22
• Resolved: 26/Apr/21 12:49

Description

jorgecarleitao offered a great way to improve the Debug/Display implementations for various Array implementations on https://github.com/apache/arrow/pull/9624#issuecomment-790976766

The only reason we are implementing to_isize/to_usize on NativeType is because we have a function to represent an array (for Display) that accepts a generic physical type T, and then tries to convert it to a isize depending on a logical type (DataType::Date). However, there is already a Many to one relationship between logical and physical types.

Thus, a solution for this is to have the `Debug` function branch off depending on the (logical) datatype, implementing the custom string representation depending on it, instead of having a loop of native type T and then branching off according to the DataType inside the loop.

I.e. instead of

for i in ... {
   match data_type {
         DataType::Date32 => represent array[i] as date
         DataType::Int32 => represent array[i] as int
   }
}

imo we should have

match data_type {
     DataType::Date32 => for i in ... {represent array[i] as date}
     DataType::Int32 => for i in ... {represent array[i] as int}
}

i.e. treat the Display as any other "kernel", where behavior is logical, not physical, type-dependent.